Apparatus and Method for Directional Resistivity Measurement While Drilling Using Slot Antenna

Abstract

An apparatus for making directional resistivity measurements of a subterranean formation includes a resistivity tool with a longitudinal axis and an outer surface, multiple slots formed on the outer surface of the resistivity tool and oriented substantially parallel to the longitude axis of the resistivity tool, and multiple wires posited in the slots and electrically connecting end walls of the slots to form magnetic dipole antennas. The mantic dipole antennas form at least one transmitter-receiver antenna group to perform transmission and reception of electromagnetic signals. A corresponding method for making directional resistivity measurements is also provided.

What is claimed is: 
     
         1 . A method for making directional resistivity measurements of a subterranean formation comprising:
 rotating a resistivity tool in a borehole;   transmitting electromagnetic signals from a first slot antenna deployed on the resistivity tool;   receiving the electromagnetic signals on a second slot antenna deployed on the resistivity tool;   extracting a sinusoidal wave from induced voltages on the second slot antenna during a rotation round of the resistivity tool;   deriving information of the orientation of a formation boundary;   extracting peak-valley amplitudes of induced voltages on the second slot antenna during the rotation round of the resistivity tool and a rotation angle; and   deriving information of distance and direction to the formation boundary.   
     
     
         2 . The method according to  claim 1  wherein the first and the second slot antennas are recessed regions formed on an outer surface of the resistivity tool with a wire posited inside. 
     
     
         3 . The method according to  claim 2  wherein the wire electrically connects an end wall of the recessed region to the center conductor of a coaxial connector at the other end of the recessed region and generates magnetic fields as a magnetic dipole. 
     
     
         4 . The method according to  claim 3  wherein the coaxial connector links the wire in the recessed region to a circuit for signal transmission. 
     
     
         5 . An magnetic dipole antenna deployed in a resistivity tool with a longitudinal axis and an outer surface, comprising;
 an indentation formed on the outer surface of the resistivity tool;   a coaxial connector deployed under the outer surface of the resistivity tool;   a wire posited in the indentation and electrically connecting an end wall of the indentation and the center conductor of the coaxial connector at the other end of the indentation; and   wherein the indentation and the wire forms a magnetic dipole to transmit or receive electromagnetic signals.   
     
     
         6 . The magnetic dipole antenna according to  claim 5  further comprises a magnetically permeable material filled in the indentation. 
     
     
         7 . The magnetic dipole antenna according to  claim 6  wherein the magnetically permeable material is a magnetic material for enhancing transmission and reception of the magnetic dipole. 
     
     
         8 . The magnetic dipole antenna according to  claim 7  wherein the magnetic material is selected form the group consisting of a ferrite material, an electrically non-conductive magnetic alloy, an iron powder, and a nickel iron alloy. 
     
     
         9 . The magnetic dipole antenna according to  claim 5  further comprises a protective material filled in the indentation. 
     
     
         10 . The magnetic dipole antenna according to  claim 9  wherein the protective material is epoxy resin. 
     
     
         11 . The magnetic dipole antenna according to  claim 5  wherein the indentation is circular shaped. 
     
     
         12 . The magnetic dipole antenna according to  claim 5  wherein the indentation is rectangular shaped. 
     
     
         13 . The magnetic dipole antenna according to  claim 5  further comprises multiple grooves formed on the outer surface and across the indentation on the resistivity tool to enhance transmission and reception of electromagnetic signals. 
     
     
         14 . The magnetic dipole antenna according to  claim 13  wherein the groove is oval shaped. 
     
     
         15 . An apparatus for making directional resistivity measurements of a subterranean formation comprising:
 a resistivity tool with a longitudinal axis and an outer surface;   multiple slots formed on the outer surface of the resistivity tool and oriented substantially parallel to the longitude axis of the resistivity tool;   multiple wires posited in the slots and electrically connecting end walls of the slots to form magnetic dipole antennas; and   wherein the mantic dipole antennas form at least one transmitter-receiver antenna group to perform transmission and reception of electromagnetic signals.   
     
     
         16 . The apparatus according to  claim 15  further comprises a coaxial connector to connect the wires with a circuit for processing the electromagnetic signals to be transmitted or received. 
     
     
         17 . The apparatus according to  claim 15  further comprises multiple grooves formed on the outer surface and cross the slots on the resistivity tool to enhance transmission and reception of the electromagnetic signals. 
     
     
         18 . The apparatus according to  claim 17  wherein the grooves are substantially transverse to the slots on the resistivity tool. 
     
     
         19 . The apparatus according to  claim 15  further comprises a magnetically permeable material filled in the slots. 
     
     
         20 . The apparatus according to  claim 15  further comprises a protective material filled in the slots.